Purification and characterization of two b-glucosidases from the thermophilic fungusThermoascus aurantiacus

b-Glucosidase from the fungusThermoascus aurantiacus grown on semi-solid fermentation medium (using ground corncob as substrate) was partially purified in 5 steps--ultrafiltration, ethanol precipitation, gel filtration and 2 anion exchange chromatography runs, and characterized. After the first anion exchange chromatography, b-glucosidase activity was eluted in 3 peaks (Gl-1, Gl-2, Gl-3). Only the Gl-2 and Gl-3 fractions were adsorbed on the gel matrix. Gl-2 and Gl-3 exhibited optimum pH at 4.5 and 4.0, respectively. The temperature optimum of both glucosidases was at 75-80C. The pH stability of Gl-2 (4.0-9.0) was higher than Gl-3 (5.5-8.5); both enzyme activities showed similar patterns of thermostability. Under conditions of denaturing gel chromatography the molar mass of Gl-2 and Gl-3 was 175 and 157 kDa, respectively. Using 4-nitrophenyl b-d-glucopyranoside as substrate,K sub(m) values of 1.17c0.35 and 1.38c0.86 mmol/L were determined for Gl-2 and Gl-3, respectively. Both enzymes were inhibited by Ag super(+) and stimulated by Ca super(2+).